GaN, which is a semiconductor material of a direct transition type having broad band gap energy of 3.4 eV, is an ideal photoelectric semiconductor material capable of realizing all the wavelengths of light ranging from the ultraviolet band to the visible light band.
There had been much difficulty in forming GaN epitaxial layers of high quality due to non-existence of a substrate, which has a lattice constant consistent with that of GaN, in the course of their growth. A resolution has now become available for fabricating a GaN device of high quality by forming a low-temperature GaN buffer layer between a substrate and a GaN device layer.
However, the GaN crystal formed by means of such method still includes much crystal defect (1×109 cm−2˜1×1010 cm−2), which becomes a bar to stable operation and lifespan of the device. In particular, such crystal defect becomes a cause of electron-hole combination, which becomes phonon dispersion without emission of light, thereby deteriorating the emitting efficiency.
To solve this problem, epitaxial lateral over-growth (ELOG) or pendeo-epitaxial growth has conventionally been used to decrease the crystal defects. However, these methods commonly pose a problem of necessitating a photolithographic process and a subsequent etching process prior to generating a GaN device layer, thereby causing contamination of the substrate and deteriorating the productivity and yield due to the separate etching process and dual growing processes.
Under the circumstances, a new method for growing GaN has become required to fabricate the GaN with a single growing process while decreasing the crystal defects.